Lithium manganese oxide-based active material

ABSTRACT

The invention provides an electrochemically active material comprising particles of spinel lithium manganese oxide having on the surface of each particle cationic metal species bound to the spinel at anionic sites of the particle surface; where the cationic metal species includes a metal selected from the group consisting of transition metals, non-transition metals having a +3 valence state, and mixtures thereof. The active material is characterized by a reduced surface area and increased capacity expressed in milliamp hour per gram as compared to the spinel alone.

FIELD OF THE INVENTION

[0001] This invention relates to electrochemical cells and batteries,and more particularly, to improved electrode active material of suchbatteries, and novel methods of synthesis.

BACKGROUND OF THE INVENTION

[0002] Lithium batteries are prepared from one or more lithiumelectrochemical cells containing electrochemically active(electroactive) materials. Such cells typically include an anode(negative electrode), a cathode (positive electrode), and an electrolyteinterposed between spaced apart positive and negative electrodes.Batteries with anodes of metallic lithium and containing metalchalcogenide cathode active material are known. The electrolytetypically comprises a salt of lithium dissolved in one or more solvents,typically nonaqueous (aprotic) organic solvents. Other electrolytes aresolid electrolytes typically called polymeric matrixes that contain anionic conductive medium, typically a metallic powder or salt, incombination with a polymer that itself may be ionically conductive whichis electrically insulating. By convention, during discharge of the cell,the negative electrode of the cell is defined as the anode. Cells havinga metallic lithium anode and metal chalcogenide cathode are charged inan initial condition. During discharge, lithium ions from the metallicanode pass through the liquid electrolyte to the electrochemical active(electroactive) material of the cathode whereupon they releaseelectrical energy to an external circuit.

[0003] It has recently been suggested to replace the lithium metal anodewith an intercalation anode, such as a lithium metal chalcogenide orlithium metal oxide. Carbon anodes, such as coke and graphite, are alsointercalation materials. Such negative electrodes are used withlithium-containing intercalation cathodes, in order to form anelectroactive couple in a cell. Such cells, in an initial condition, arenot charged. In order to be used to deliver electrochemical energy, suchcells must be charged in order to transfer lithium to the anode from thelithium-containing cathode. During discharge the lithium is transferredfrom the anode back to the cathode. During a subsequent recharge, thelithium is transferred back to the anode where it reintercalates. Uponsubsequent charge and discharge, the lithium ions (Li⁺) are transportedbetween the electrodes. Such rechargeable batteries, having no freemetallic species are called rechargeable ion batteries or rocking chairbatteries. See U.S. Pat. Nos. 5,418,090; 4,464,447; 4,194,062; and5,130,211.

[0004] Preferred positive electrode active materials include LiCoO₂,LiMn₂O₄, and LiNiO₂. The cobalt compounds are relatively expensive andthe nickel compounds are difficult to synthesize. A relativelyeconomical positive electrode is LiMn₂O₄, for which methods of synthesisare known, and involve reacting generally stoichiometric quantities of alithium-containing compound and a manganese containing compound. Thelithium cobalt oxide (LiCoO₂), the lithium manganese oxide (LiMn₂O₄),and the lithium nickel oxide (LiNiO₂) all have a common disadvantage inthat the charge capacity of a cell comprising such cathodes suffers asignificant loss in capacity. That is, the initial capacity available(amp hours/gram) from LiMn₂O₄, LiNiO₂, and LiCoO₂ is less than thetheoretical capacity because less than 1 atomic unit of lithium engagesin the electrochemical reaction. Such an initial capacity value issignificantly diminished during the first cycle operation and suchcapacity further diminishes on every successive cycle of operation. Thespecific capacity for LiMn₂O₄ is at best 148 milliamp hours per gram. Asdescribed by those skilled in the field, the best that one might hopefor is a reversible capacity of the order of 110 to 120 milliamp hoursper gram. Obviously, there is a tremendous difference between thetheoretical capacity (assuming all lithium is extracted from LiMn₂O₄)and the actual capacity when only 0.8 atomic units of lithium areextracted as observed during operation of a cell. For LiNiO₂ and LiCoO₂only about 0.5 atomic units of lithium is reversibly cycled during celloperation. Many attempts have been made to reduce capacity fading, forexample, as described in U.S. Pat. No. 4,828,834 by Nagaura et al.However, the presently known and commonly used, alkali transition metaloxide compounds suffer from relatively low capacity. Therefore, thereremains the difficulty of obtaining a lithium-containing chalcogenideelectrode material having acceptable capacity without disadvantage ofsignificant capacity loss when used in a cell.

[0005] Capacity fading is well known and is calculated according to theequation given below. The equation is used to calculate the first cyclecapacity loss. This same equation is also used to calculate subsequentprogressive capacity loss during subsequent cycling relative back to thefirst cycle capacity charge reference. $\frac{\begin{matrix}\left( {\left( {{FC}\quad {charge}\quad {capacity}} \right) -} \right. \\{\left. \left( {{FC}\quad {discharge}\quad {capacity}} \right) \right) \times 100\%}\end{matrix}}{{FC}\quad {charge}\quad {capacity}}$

[0006] In U.S. Pat. No. 4,828,834 Nagaura et al. attempted to reducecapacity fading by sintering precursor lithium salt and MnO₂ materialsand thereby forming an LiMn₂O₄ intercalation compound. However,Nagaura's LiMn₂O₄ compounds were not fully crystallized spinelelectrodes and suffered from a very low capacity. Despite the aboveapproaches, there remains the difficulty of obtaining lithium manganeseoxide based electrode materials having the attractive capacity of thebasic spinel Li_(x)Mn₂O₄ intercalation compound, but without itsdisadvantage of significant capacity loss on progressive cycling.

SUMMARY OF THE INVENTION

[0007] The present invention provides a composition suitable for use asan electrochemically active material for an electrochemical cell. Thecomposition comprises particles of spinel lithium manganese oxide havingon the surface of the particles ionic metal species bound to the spinelat oppositely charged respective ionic sites of the spinel particlesurface. The ionic metal species preferably includes a transition metal.Alternatively, the ionic metal species includes a non-transition metalcapable of a +3 valence state. The ionic species may contain mixtures ofthe foregoing metals. Cationic metal species bound to the spinelparticle surface include, but are not limited to, metal cation, metaloxide cation, and metal phosphate cation.

[0008] In a preferred method, the composition comprising the spinellithium manganese oxide having ionic species bound thereto is preparedby decomposing or melting a precursor metal compound on the surface ofthe spinel particles, thereby giving rise to the cationic metal species.

[0009] The spinel lithium manganese oxide treated for improved resultsby the method of the invention is known to have the nominal formulaLi₁Mn₂O₄. Such spinel lithium manganese oxide compounds may vary in therelative proportion of lithium, manganese, and oxygen while maintainingidentity as a spinel lithium manganese oxide insertion compound. Theinvention is not limited to any particular formulation for a spinellithium manganese oxide. However, advantageous results are obtained whenthe spinel lithium manganese oxide is represented by the nominal formulaLi_(1+x)Mn_(2−x)O₄ where x is a range of about −0.2 to about +0.5; andmore preferably where x is greater than zero and up to about 0.5.

[0010] The treated spinel lithium manganese oxide is prepared as anelectrode by mixing it with a binder and optionally with an electricallyconductive material and forming it into an electrical structure.

[0011] The composite spinel manganese oxide particles having the metalspecies bound thereto is prepared by first forming a mixture comprisingthe lithium manganese oxide particles and the metal compound. Themixture may be formed by mixing lithium manganese oxide powder and metalcompound powder. Alternately, the metal compound (metal salt) isdissolved in a suitable solvent, then the lithium manganese oxideparticles are thoroughly wetted by the solution before reaction.Reaction is conducted by heating the mixture containing the spinelparticles and the metal compound for a time and at a temperaturesufficient to form a decomposition product of the metal compound on thesurface of the particles. In an alternative embodiment, the metalcompound is reacted at the surface of the spinel while undergoinglimited, very little, or no decomposition. For example, when the metalcompound is a phosphate salt, the phosphate salts retain their phosphategroups, and the heating serves to chemically disperse and adhere thephosphate to the spinel.

[0012] It is preferred that the heating to cause reaction between themetal compound and the surface of the lithium manganese oxide beconducted at a temperature in a range from about 20° C. to about 800°C., desirably 200° C. to about 750° C., more desirably 2000° C. to about700° C., in an air atmosphere for at least about ½ hour and up to about6 hours. Since any amount of the metal compound will improve thecharacteristics of the LMO, there is no practical lower limit to theamount to be added as long as the amount is greater than zero. It ispreferred that the amount of metal compound included with the lithiummanganese oxide in the mixture be up to about 10 wt. % of the mixturewith the lithium manganese oxide constituting the balance.

[0013] Objects, features, and advantages of the invention include animproved electrochemical cell or battery based on lithium which hasimproved charging and discharging characteristics, a large dischargecapacity, and which maintains its integrity during cycling. Anotherobject is to provide a cathode active material which combines theadvantages of large discharge capacity and with relatively lessercapacity fading. It is also an object of the present invention toprovide positive electrodes having active materials which operate withgood performance over a relatively broad temperature range. Anotherobject is to provide a method for forming cathode active material whichlends itself to commercial scale production providing for ease ofpreparing large quantities.

[0014] These and other objects, features, and advantages will becomeapparent from the following description of the preferred embodiments,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is an EVS (electrochemical voltage spectroscopy)voltage/capacity profile for a cell embodying the specially treatedlithium manganese oxide (LMO) material of the invention in combinationwith a lithium metal counter electrode in an electrolyte comprising amixture of ethylene carbonate and dimethyl carbonate and including a onemolar concentration of LiPF₆ salt. The lithium manganese oxide basedelectrode and the lithium metal counter electrode are maintained spacedapart by a separator of glass fiber which is interpenetrated by thesolvent and the salt. The conditions of cycling are +10 mV, betweenabout 3.0 and 4.4 volts, and the critical current density is less thanor equal to about 0.08 mA/cm². The treated LMO was prepared usinglithium aluminum chloride in a weight proportion of 4% LiAlCl₄ and 96%LMO.

[0016]FIG. 2 is an EVS differential capacity plot for the cell asdescribed in connection with FIG. 1.

[0017]FIG. 3 shows the results of an x-ray diffraction analysis of thespecially treated lithium manganese oxide prepared according to theinvention, using CuKaα with λ=1.5418 angstroms.

[0018]FIG. 4 contains an x-ray diffraction analysis of conventional,untreated LMO, as received from a vendor.

[0019]FIG. 5 is an EVS voltage/capacity profile for a cell containinglithium manganese oxide material treated with cobalt nitrate to providethe active material for a positive electrode of the invention incombination with a lithium metal counter-electrode in an electrolyte asdescribed with respect to FIG. 1 above. The conditions of the test areas described with respect to FIG. 1 above. The treated LMO was preparedusing a weight proportion of 4% cobalt nitrate and 96% LMO.

[0020]FIG. 6 is an EVS differential capacity plot for the cell asdescribed in connection with FIG. 5.

[0021]FIG. 7 is an EVS voltage/capacity profile for a cell containinglithium manganese oxide material treated with cobalt nitrate to providethe active material for a positive electrode of the invention incombination with a lithium metal counter-electrode in an electrolyte asdescribed with respect to FIG. 1 above. The conditions of the test areas described with respect to FIG. 1 above. The treated LMO was preparedusing a weight proportion of 5.3% cobalt nitrate and 96% LMO.

[0022]FIG. 8 is an EVS differential capacity plot for the cell asdescribed in connection with FIG. 7.

[0023]FIG. 9 is an EVS voltage/capacity profile for a cell containinglithium manganese oxide material treated with chromium acetate toprovide the active material for a positive electrode of the invention incombination with a lithium metal counter-electrode in an electrolyte asdescribed with respect to FIG. 1 above. The conditions of the test areas described with respect to FIG. 1 above. The treated LMO was preparedusing a weight proportion of 4% chromium acetate and 96% LMO.

[0024]FIG. 10 is an EVS differential capacity plot for the cell asdescribed in connection with FIG. 9.

[0025]FIG. 11 is a diagrammic representation of a typical laminatedlithium-ion battery cell structure.

[0026]FIG. 12 is a diagrammic representation of a typical multicellbattery cell structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The treated lithium manganese oxide of this invention is obtainedessentially as a result of the thermal dispersion of a metal compoundonto the surface of the lithium manganese oxide and preferablyconcurrently the decomposition of said metal compound on the surface.This is accomplished by heating the dispersed metal compound at anelevated temperature after the metal compound and the LMO have beenbrought into contact with each other. It is believed that the treatedlithium manganese oxide (LMO) made in accordance with this inventiondiffers fundamentally from the lithium manganese oxide known in the art.This difference is reflected in the treated lithium manganese oxidedistinguished electrical chemical performance in a cell and alsodistinguished by the process by which the treated LMO is prepared.

[0028] Many metal compounds or their mixtures can be used, and metalsalts are preferred. One group of desirable metal compounds aretransition metal compounds. Another group of desirable metal compoundsare non-transition metal compounds which contain a metal capable of a +3valence state, such as aluminum. Some representative examples of themetal compounds which can be suitably utilized in the practice of thisinvention include, for example, LiAlCl₄ (lithium aluminum chloride),nitrates, including Al(NO₃)₃ (aluminum nitrate), Cr₂(OCOCH₃)₄ (chromiumacetate), NiCO₃ (nickel carbonate), Co(NO₃)₂ (cobalt nitrate), CoCO₃(cobalt carbonate), and ZrOCl₂ (zirconium aluminum chloride) Mixtures ofthese and similar compounds may also be used. An example is the mixture:LiNO₃, Co(NO₃)₂, Al(NO₃)₃, NiCO₃. Other examples can be found in Table1.

[0029] Desirable metal compounds are transition metals with nitrates,acetates, carbonates, and phosphates; and especially preferred are thenitrates; with cobalt nitrate being most preferred. As the lithiummanganese oxide (LMO) used to produce the treated LMO of this invention,a range of formulations may be used consistent with the basic lithiummanganese oxide spinel of the nominal general formula LiMn₂O₄.

[0030] The nominal general formula LiMn₂O₄ represents a relativelynarrow range of spinel lithium manganese oxide compounds (referred to asLMO) which have stoichiometry that varies somewhat in the relativeproportion of lithium, manganese and oxygen, but still having the spinelstructure. Oxygen deficient spinels are not favored here. Relativelylithium rich spinels are favored here. One desirable range ofcompositions is the spinel formula Li_(1+x)Mn_(2−x)O₄ where O<x≦x0.5.Lithium deficient spinels with x less than O (i.e., −0.2) are alsoknown. In the experiments below, a spinel lithium manganese oxide had asurface area of 0.9 m²/g; average particle size of 30 microns; lithiumcontent of 4.1%, corresponding to Li_(1.07); less than 1% impurities andlattice parameter of 8.22.

[0031] Such lithium manganese oxide compounds must have a suitably highsurface area and the ability to be coated with metal compound which isdispersed and decomposed thereon. It is desirable in the preparation ofthe treated LMO according to the invention, that the surface area of theLMO is between about 0.5 and 2.5 m²/g and that the range of compositionwould be lithium content of 1.02≦x ≦1.10.

[0032] In the process for the preparation of the treated LMO accordingto the invention, a mixture containing the metal compound and the LMO isused. In a preferred embodiment of the invention, the mixture isprepared simply by mixing mechanically a powder form of the metalcompound and a powder form of the LMO. The mixture can also be obtainedby adding to the LMO a solution or suspension of the metal compound in asuitable solvent. Thereafter, the solvent is removed from the resultingmixture by heating, vacuum, simple evaporation, or other equivalentmeans known in the art.

[0033] Representative examples of solvents that can be suitably usedinclude, acetone and primary or secondary alcohols having one to sevencarbon atoms. One particularly suitable solvent is methanol.

[0034] In the above-described mixture containing the metal compound andthe LMO, the amount of metal compound is desirably from 0.1 to 10%, moredesirably from 0.5 to 5%, and preferably 1 to 4% by weight of themixture, with the LMO constituting the balance.

[0035] The prepared mixture containing the metal compound and the LMO issubjected to heating. This heating step is carried out at a temperaturehigh enough to initiate the thermal dispersion of the metal compoundonto the surface of individual particles of the LMO. The temperature isalso desirably high enough to at least partially decompose the metalcompound at the surface. Preferably, the temperature is high enough toessentially completely decompose the metal compound, leaving behind thepositive cation of the metal which formerly constituted the metalcompound. The extent of decomposition depends upon the metal compoundused and the desired result. Metal phosphate compounds do notsignificantly decompose, but do appear to be bound at the spinelsurface, and form a reacted product with the spinel at the surface. Inthe case where a mixed metal compound is used, cations from differentmetal elements may remain after decomposition. However, the heatingtemperature is below the temperature at which the LMO will bedecomposed, and the heating temperature is below the melting point ofthe LMO. Heating is conducted for a duration of time sufficient tothermally disperse the metal compound onto the surface of the LMO, andas stated above, is preferably sufficient to at least partiallydecompose it. It is considered that complete decomposition is achievedwhen the only residual from the metal compound remaining on the surfaceis a metal cation which originated from the compound. The exceptionalcase being as per the phosphate example.

[0036] In the practice of the invention, the heating step isconveniently performed at a temperature in the range of about 200° C. toabout 850° C. for a period of time from about 0.5 to about 12 hours.Desirably the heating is conducted at about 200° C. to about 800° C.,more desirably 200°C. to about 750° C., and most desirably at about 200°C. to about 700° C. In one embodiment, the heating is conducted at atemperature in the range of about 400 to about 500° C. and for a time ofabout 4 to 5 hours. The conditions depend, in part, on the metalcompound used.

[0037] The heating step can be conveniently conducted in a suitableatmosphere such as ambient air. Advantageously, special conditions suchas vacuum, inert or oxygen content control are not needed.

[0038] The heating should be carried out for a time period sufficient tocause a surface-area-reducing effect on the LMO. It is believed that thegreater the amount of the residual metal ion remaining after dispersionand decomposition, the greater will be the surface area reductioneffect.

[0039] Positive electrode active materials were prepared and tested todetermine physical, chemical and electrochemical features. The resultsare reported in FIGS. 1 to 10. Typical cell configurations will bedescribed with reference to FIGS. 11 and 12.

[0040] A typical laminated battery cell structure 10 is depicted in FIG.11. It comprises a negative electrode side 12, a positive electrode side14, and an electrolyte/separator 16 therebetween. Negative electrodeside 12 includes current collector 18, and positive electrode side 14includes current collector 22. A copper collector foil 18, preferably inthe form of an open mesh grid, upon which is laid a negative electrodemembrane 20 comprising an intercalation material such as carbon orgraphite or low-voltage lithium insertion compound, dispersed in apolymeric binder matrix. An electrolyte separator film 16 membrane ofplasticized copolymer is positioned upon the electrode element and iscovered with a positive electrode membrane 24 comprising a compositionof a finely divided lithium intercalation compound in a polymeric bindermatrix. An aluminum collector foil or grid 22 completes the assembly.Protective bagging material 40 covers the cell and prevents infiltrationof air and moisture.

[0041] In another embodiment, a multicell battery configuration as perFIG. 12 is prepared with copper current collector 51, negative electrode53, electrolyte/separator 55, positive electrode 57, and aluminumcurrent collector 59. Tabs 52 and 58 of the current collector elementsform respective terminals for the battery structure.

[0042] The relative weight proportions of the components of the positiveelectrode are generally: 50-90% by weight active material; 5-30% carbonblack as the electric conductive diluent; and 3-20% binder chosen tohold all particulate materials in contact with one another withoutdegrading ionic conductivity. Stated ranges are not critical, and theamount of active material in an electrode may range from 25-95 weightpercent. The negative electrode comprises about 50-95% by weight of apreferred graphite, with the balance constituted by the binder. Atypical electrolyte separator film comprises approximately two partspolymer for every one part of a preferred fumed silica. Before removalof the plasticizer, the separator film comprises about 20-70% by weightof the composition; the balance constituted by the polymer and fumedsilica in the aforesaid relative weight proportion. The conductivesolvent comprises any number of suitable solvents and salts. Desirablesolvents and salts are described in U.S. Pat. No. 5,643,695 and5,418,091. One example is a mixture of EC:DMC:LiPF₆ in a weight ratio ofabout 60:30:10.

[0043] Solvents are selected to be used individually or in mixtures, andinclude dimethyl carbonate (DMC), diethylcarbonate (DEC),dipropylcarbonate (DPC), ethylmethylcarbanate (EMC), ethylene carbonate(EC), propylene carbonate (PC), butylene carbonate, lactones, esters,glymes, sulfoxides, sulfolanes, etc. The preferred solvents are EC/DMC,EC/DEC, EC/DPC and EC/EMC. The salt content ranges from 5% to 65% byweight, preferably from 8% to 35% by weight.

[0044] Those skilled in the art will understand that any number ofmethods are used to form films from the casting solution usingconventional meter bar or doctor blade apparatus. It is usuallysufficient to air-dry the films at moderate temperature to yieldself-supporting films of copolymer composition. Lamination of assembledcell structures is accomplished by conventional means by pressingbetween metal plates at a temperature of about 120-160° C. Subsequent tolamination, the battery cell material may be stored either with theretained plasticizer or as a dry sheet after extraction of theplasticizer with a selective low-boiling point solvent. The plasticizerextraction solvent is not critical, and methanol or ether are oftenused.

[0045] Separator membrane element 16 is generally polymeric and preparedfrom a composition comprising a copolymer. A preferred composition isthe 75 to 92% vinylidene fluoride with 8 to 25% hexafluoropropylenecopolymer (available commercially from Atochem North America as KynarFLEX) and an organic solvent plasticizer. Such a copolymer compositionis also preferred for the preparation of the electrode membraneelements, since subsequent laminate interface compatibility is ensured.The plasticizing solvent may be one of the various organic compoundscommonly used as solvents for electrolyte salts, e.g., propylenecarbonate or ethylene carbonate, as well as mixtures of these compounds.Higher-boiling plasticizer compounds such as dibutyl phthalate, dimethylphthalate, diethyl phthalate, and tris butoxyethyl phosphate areparticularly suitable. Inorganic filler adjuncts, such as fumed aluminaor silanized fumed silica, may be used to enhance the physical strengthand melt viscosity of a separator membrane and, in some compositions, toincrease the subsequent level of electrolyte solution absorption.

[0046] In the construction of a lithium-ion battery, a current collectorlayer of aluminum foil or grid is overlaid with a positive electrodefilm, or membrane, separately prepared as a coated layer of a dispersionof intercalation electrode composition. This is typically anintercalation compound such as LiMn₂O₄ (LMO), LiCoO₂, or LiNiO₂, powderin a copolymer matrix solution, which is dried to form the positiveelectrode. An electrolyte/seperator membrane is formed as a driedcoating of a composition comprising a solution containing VdF:HFPcopolymer and a plasticizer solvent is then overlaid on the positiveelectrode film. A negative electrode membrane formed as a dried coatingof a powdered carbon or other negative electrode material dispersion ina VdF:HFP copolymer matrix solution is similarly overlaid on theseparator membrane layer. A copper current collector foil or grid islaid upon the negative electrode layer to complete the cell assembly.Therefore, the VdF:HFP copolymer composition is used as a binder in allof the major cell components, positive electrode film, negativeelectrode film, and electrolyte/separator membrane. The assembledcomponents are then heated under pressure to achieve heat-fusion bondingbetween the plasticized copolymer matrix electrode and electrolytecomponents, and to the collector grids, to thereby form an effectivelaminate of cell elements. This produces an essentially unitary andflexible battery cell structure.

[0047] Examples of forming cells containing metallic lithium anode,intercalation electrodes, solid electrolytes and liquid electrolytes canbe found in U.S. Pat. Nos. 4,668,595; 4,830,939; 4,935,317; 4,990,413;4,792,504; 5,037,712; 5,262,253; 5,300,373; 5,435,054; 5,463,179;5,399,447; 5,482,795 and 5,411,820; each of which is incorporated hereinby reference in its entirety. Note that the older generation of cellscontained organic polymeric and inorganic electrolyte matrix materials,with the polymeric being most preferred. The polyethylene oxide of U.S.Pat. No. 5,411,820 is an example. More modern examples are the VDF:HFPpolymeric matrix. Examples of casting, lamination and formation of cellsusing VdF:HFP are as described in U.S. Pat. Nos. 5,418,091; 5,460,904;5,456,000; and 5,540,741; assigned to Bell Communications Research, eachof which is incorporated herein by reference in its entirety.

[0048] As described earlier, the electrochemical cell which utilizes thenovel solvent of the invention may be prepared in a variety of ways. Inone embodiment, the negative electrode may be metallic lithium. In moredesirable embodiments, the negative electrode is an intercalation activematerial, such as, metal oxides and graphite. When a metal oxide activematerial is used, the components of the electrode are the metal oxide,electrically conductive carbon, and binder, in proportions similar tothat described above for the positive electrode. In a preferredembodiment, the negative electrode active material is graphiteparticles. For test purposes, test cells were fabricated using lithiummetal electrodes. When forming cells for use as batteries, it ispreferred to use an intercalation metal oxide positive electrode and agraphitic carbon negative electrode. Various methods for fabricatingelectrochemical cells and batteries and for forming electrode componentsare described herein. The invention is not, however, limited by anyparticular fabrication method as the novelty lies in the treated LMOactive material.

EXAMPLE 1 Preparation Usina 96:4 by Weight LMO:LiAlCl₄

[0049] In this example, treated lithium manganese oxide was preparedusing a lithium aluminum chloride compound. The lithium manganese oxidein this example had the nominal formula Li _(1.08)Mn_(1.92)O₄ and wasobtained from Japan Energy Corporation. The lithium aluminum chloridehad the formula LiAlCl₄. It was obtained from Aldrich Chemical Company.The lithium aluminum chloride is known to be hygroscopic. This requiredthat the grinding of the lithium aluminum chloride powder to the desiredparticle size be done under argon. The milled lithium aluminum chlorideand the lithium manganese oxide powders were mixed and milled togetherto achieve a well intermingled mixture. The objective is to achieve anintermingled mixture which is as close to homogeneous as possible. Inthis example, the mixture constituted 4% by wt. of the lithium aluminumtetrachloride and 96% by wt. of the lithium manganese oxide. Theintermingled particles were then heated in a furnace at a temperature ofabout 450° C. for a time of about 1 hour. The heating was conducted inair, and no special atmosphere was required. Heating at this temperatureand time was found to be sufficient to decompose the lithium aluminumchloride compound. After heating for 1 hour, the product was allowed tocool. The rate of cooling did not appear to be critical and it waspossible to simply remove the product from the oven and let it cool downto room temperature. It is also possible to allow it to cool in the ovenonce the heat has been turned off. Quenching by cooling at roomtemperature is convenient but does not appear to be critical.

[0050] The active material, the treated lithium manganese oxide of theinvention, prepared according to this example, was tested in a testcell. Positive electrode, as tested, comprised the active material at87% by wt.; carbon black (Super-P type) 4% by wt.; and 9% by wt.polyvinylidene-flouride-co-hexafluoropropane type binder. Theelectrolyte was a 2 to 1 weight ratio of EC and DMC solvents andcontained 1 molar LiPF₆ type salt. The separator was a glass fiber type.The counter electrode was metallic lithium. The current density of thetest cell was 0.08 milliamp hours per cm². The test cell was based on2.4 cm² positive electrode with active material loading of about 34 to36 milligrams per cm². The capacity was determined under constantcurrent cycling ±0.08 mA/cm² at room temperature. The cell was cycledbetween about 3 and about 4.3 volts with performance as shown in theFigures.

[0051]FIG. 1 shows a voltage profile of the test cell, based on thetreated lithium manganese oxide (LMO) positive electrode active materialof the invention, and using a lithium metal counter electrode asdescribed in the examples. The data shown in FIG. 1 is based on theElectrochemical Voltage Spectroscopy (EVS) technique. Electrochemicaland kinetic data were recorded using the Electrochemical VoltageSpectroscopy (EVS) technique. Such technique is known in the art asdescribed by J. Barker in Synth, Met 28, D217 (1989); Synth. Met. 32, 43(1989); J. Power Sources, 52, 185 (1994); and Electrochemical Acta, Vol.40, No. 11, at 1603 (1995).

[0052]FIG. 1 clearly shows and highlights the very good performance andreversibility of the treated lithium manganese oxide of the invention.The positive electrode contained about 85 milligrams of the treatedactive material. The total electrode weight including the binder andconductive carbon diluent was about 98 milligrams. The positiveelectrodes showed a performance of about 131 milliamp hours per gram onthe first discharge. This means that the electrode provided a specificcapacity of 131 milliamp hours per gram out (lithium extracted). Then onrecharge of this active material, on the order of 123 milliamp hours pergram was observed in (lithium inserted). On subsequent cycling, goodperformance continued to be exhibited. In a re-test of this sample, thepositive electrode provided 130 mAh/gm on first discharge (lithiumextracted) and 122 mAh/gm on the second cycle discharge.

[0053]FIG. 2 is an EVS differential capacity plot based on FIG. 1. Ascan be seen from FIG. 2, the relatively symmetrical nature of the peaksindicates good electrical reversibility, there being no peaks related toirreversible reactions, since all peaks above the axis (cell charge)have corresponding peaks below the axis (cell discharge), and there isessentially no separation between the peaks above and below the axis.The peaks also show an indication of good crystallinity from their sharpappearance demonstrating a good crystallinity of the active material.

[0054]FIG. 3 shows the results of an x-ray diffraction analysis of thetreated lithium manganese oxide prepared according to the invention. Thex-ray diffraction was conducted using CuKα type radiation. Thediffraction analysis shown in FIG. 3 is nearly identical to conventionallithium manganese oxide (FIG. 4) of the nominal formula Li₁Mn₂O₄ exceptfor the presence of the added metal compound and some variations in theamount of lithium. This minor variation in the amount of lithium iswithin the variation expected when conventional lithium manganese oxideis prepared. This indicates that the structure of the treated LMO of theinvention is similar, and essentially identical to, the basic spinelstructure of conventional Li₁Mn₂O₄. This is advantageous because thespinel structure is known to reversibly intercalate lithium at a higherrate compared to other structures such as tetragonal lithium manganeseoxide. FIG. 4 contains an x-ray diffraction analysis of conventionallithium manganese oxide (Li₁Mn₂O₄) prepared according to conventionaltechniques and as received from the vendor. See U.S. Pat. No. 5,770,018,incorporated by reference herein in its entirety, for a description ofconventional LMO. As can be seen by comparing FIGS. 3 and 4, the productof the invention has the same spinel structure as the conventionallithium manganese oxide, except that the product of the invention hasthe metal added to its surface. The a-axis parameter of the spinelproduct of the invention is 8.2330. This further demonstrates itssimilarity to conventional lithium manganese oxide having a similara-axis parameter. Since this is a cubic structure, the other axescorrespond and are all 90 degrees with respect to one another. Thesefeatures are the same as conventional lithium manganese oxide.

[0055] Further referring to FIG. 3 and Table 2, additional informationis provided showing that the amount of lithium corresponds to 0.999atomic unit with the peak at 18.668 and a full width at half max (FWHM)of about 0.1007. The amount of lithium present in the treated compoundproportionately would be expected to change in accordance with theatomic amount of other metal, here aluminum, deposited on the surface.

EXAMPLE 2 97:3 LMO:LiAlCl₄

[0056] The procedure of Example 1 was followed except that the weigh:percent of the lithium manganese oxide and the lithium aluminum chloridewere changed. In this example, 3% by wt. lithium aluminum tetrachloridewas used and 97 wt. % lithium manganese oxide was used. As shown inTable 2, this example provided a slightly increased amount of lithium,but the cell parameters and peaks essentially remained unchanged. Herecycling performance was also good.

EXAMPLE 3 98:2 LMO: LiAlCl₄

[0057] The method of Example 1 was followed except that 2 wt. % lithiumaluminum tetrachloride was combined with 98% lithium manganese oxidewhich was then heat treated in the manner as described with respect toExample 1. With reference to Table 2, it can be seen that the atomicamount of lithium present in this product was slightly increasedcompared to the prior examples since a lesser amount of the metalcompound was used.

EXAMPLE 4 99:1 LMO:LiAlCl₄

[0058] In this example, 1% by wt. lithium aluminum tetrachloride wascombined with 99% by wt. lithium manganese oxide. The trends asdescribed with respect to earlier examples continued to be followeddemonstrating that the spinel structure was maintained.

[0059] Still additional formulations of lithium aluminum tetrachlorideand lithium manganese oxide were prepared as shown in Table 2 anddesignated as Examples PTC1-2, PTC1-14, and PTC-15 having respectively4, 2, and 10 wt. % a lithium aluminum tetrachloride. As per the latticeparameters for all the foregoing examples, the spinel structure waspreserved. Based upon the cycling performance of the 10% by wt. metalcompound additive case, it did not appear that this significant amountof additive is required in order to improve performance. cl EXAMPLE 5

98:2 LMO:Co₃(PO₄)₂

[0060] The method of Example 1 was followed except that the metalcompound was cobalt phosphate. In this example, 2% by wt. cobaltphosphate was combined with the aforesaid conventional lithium manganeseoxide obtained from the vendor. Heating was conducted at a temperatureof about 200° C. for about 2 hours time. Good cycling performance wasdemonstrated. As can be seen by reference to Table 2, the spinelstructure was also maintained when the metal compound used was cobaltphosphate.

EXAMPLE 6 Al(NO₃)₃; 4 Wt. % and 2.36 Wt. %

[0061] The method of Example 1 was followed except that the metalcompound added to the lithium manganese oxide was aluminum nitrate. Inthis example, two formulations were prepared. One formulation contained4% by wt. aluminum nitrate and 96% by wt. lithium manganese oxide. Theother formulation contained 2.35% by wt. aluminum and the balancelithium manganese oxide. The two powders were heated together as per thesame method as described with respect to Example 1, and heating wasconducted at a temperature of 450° C. for about 2 hours. Reasonably goodcycling performance was demonstrated and the spinel structure wasmaintained. Another batch at 4% was made and the surface area was 2.1(again very high) It seems likely that Al having a 3+ valence makesadditional oxide; compared to the transition metals with 2+ as thepreferred valence.

EXAMPLE 7 Cr₂(OCOCH₃)₄; 3.08 Wt. % and 2.04 Wt. %

[0062] The method of Example 1 was followed except the metal compoundused was chromium acetate. Two formulations were prepared. One contained3.08 wt. % chromium acetate, the balance lithium manganese oxide; andthe other contained 2.04 wt. % chromium acetate with the balance lithiummanganese oxide. Each formulation was heated to about 450° C. for about4 hours time to disperse the chromium compound on the particles of thelithium manganese oxide and to achieve decomposition of the chromiumacetate thereon. As can be seen from Table 2, the surface area wasconsiderably reduced. Cell performance was reasonably good. (See FIGS. 9and 10).

EXAMPLE 8 NiCO3; 3.06 Wt. % and 2.04 Wt. %

[0063] The method of Example 1 was followed except the metal compoundused was nickel carbonate. Two formulations were prepared. One contained3.06 wt. % nickel carbonate, the balance lithium manganese oxide; andthe other contained 2.04 wt. % nickel carbonate with the balance lithiummanganese oxide. Each formulation was heated treated to disperse thenickel compound on the particles of the lithium manganese oxide and toachieve decomposition of the nickel carbonate thereon. As can be seenfrom Table 2, cell performance was reasonably good.

EXAMPLE 9 Co(NO₃)₂; 5.30, 4.00, 10, and 3.00 Wt. %

[0064] The method of Example 1 was followed except the metal compoundused was cobalt nitrate. Four formulations were prepared, respectivelycontaining 5.30, 4.00, 10, and 3.00 wt % cobalt nitrate, and the balancelithium manganese oxide, respectively. Each formulation was heatedtreated to disperse the cobalt compound on the particles of the lithiummanganese oxide and to achieve decomposition of the cobalt nitratethereon. As can be seen from Table 2, cell performance ranged from goodto very high capacity. One test revealed positive electrode performanceof 137 mAh/g on first discharge (lithium out) and on subsequent cyclinggood performance was also observed. X-ray data for the 3 wt. % cobaltcarbonate/97 wt. % LMO treated sample revealed 8.2144 angstrom latticeparameter consistent with the conventional spinel. (See FIGS. 5-8).

EXAMPLE 10

[0065] In this example, the method of Example 1 was followed except thatheating was conducted at different temperatures using a rotary oven(tube furnace), and the constituents heated were as stated in Table 3.The spinel, before treatment, was Li_(1.08)Mn₂O₄ with a surface area of0.91 m²/g. This spinel was treated with varying amounts of metalcompounds under the conditions given in Table 3. In all cases, thesurface area was reduced; the capacity was very good and maintained onthe 2nd cycle; oxygen depletion was minimized; and the lithium contentwas maintained within an acceptable range. These results are impressivegiven that the heating temperature was 650° C. to 775° C., and suchelevated temperatures are often associated with oxygen depletion. TABLE1 LiAlCl₄ lithium aluminum chloride Al(NO₃)₃ aluminum nitrateNH₄Al(SO₄)₂ ammonium aluminum sulfate Cr₂(OCOCH₃)₄ chromium acetate(NH₄)₂CrO₄ ammonium chromate NiCO₃ nickel carbonate Co(NO₃)₂ cobaltnitrate Cr₂O₃ chromium oxide LiNO₃ & Al(NO₃)₃ ZrOCl₂ zirconiumdichloride oxide LiNO₃/Co(NO₃)₂/Al(NO₃)₃/NiCO₃Cr₂(OCOCH₃)₄/Al(NO₃)₃/NiCO₃ CoCO₃ cobalt carbonate Co(PO₄)₂ cobaltphosphate Co(NO₃)₂/NiCO₃ Ni₃(PO₄)₂ nickel phosphate Li₃PO₄ lithiumphosphate Co(OH)₂ cobalt hydroxide fmc 5.1 fmc 5.1/Co(NO₃)₂ fmc5.1/CuSO₄ fmc 5.1/Li₂CO₃

[0066] TABLE 2 1st Wt/% TGA Wt. Xray s.a. Cycle 2nd Lot # Additive %Loss Lattice Li(x) Peak Fwhm M2/gr s.pH Cap Cycle LMO pristine 0 08.2195 1.067 18.735 0.1482 0.9 8.52 PTC1 rxn w/ LiAlCl₄ ptc1-1 4 8.23300.999 18.668 0.1007 131 121 ptc1-1 4 130 122 ptc1-3 3 0.75 8.2317 1.00518.697 0.1024 0.751 6.22 126 119 ptc1-4 2 8.2290 1.019 18.823 0.10610.864 6.69 126 122 ptc1-5 1 8.2239 1.045 18.776 0.1075 1.023 7.02 113118 ptc1-2 4 0.9 8.2263 1.033 18.679 0.1010 0.644 6.86 122 119 ptc1-14 299.47 8.2216 1.056 119 116 ptc1-15 10 0.906 7.22 109 103 PTC15-3 rxn w/Co₃ (PO₄)₂ ptc15-3 2 8.2277 1.025 18.689 0.1111 0.5997 — 139 123 PTC3rxn w/Al (NO₃)₃ ptc3-1 4 8.2178 1.075 18.679 0.1113 3.4264 8.92 107 105ptc3-2 2.36 8.38 112 113 PTC4¹ rxn w/ Cr₂(OCOCH₃)₄ ptc5-1 3.08 0.6908.42 113 114 ptc5-3 2.04 114 113 PTC7² rxn w/ NiCO₃ ptc7-1 3.06 115 112ptc7-2 2.04 118 114 PTC8^(3 rxn w/) Co(NO₃)₂ ptc8-1 5.30 0.745 10.44 123120 ptc8-2 4.00 137 126 ptc8-3 10 0.950 8.69 108 105 ptc8-4⁴ 3.00 8.21441.093 PTC10 rxn w/LiNO₃ and Al (NO₃)₃ ptc10-1 0.14 8.2112 1.109 19.9120.1496  97  99 PTC11 rxn w/ ZrOCl₂ ptc11-1 8.2217 1.056 0.926 7.75 121119 PTC12 rxn w/LiNO₃/ Co(NO₃)₂/ Al(NO₃)₃/NiCO₃ ptc12 -1  89  90 PTC14CoCO3 ptc14-1 4 120 116

[0067] TABLE 3 Rotary Oven Residence Feed Rate Surface Capacity % OxygenLi_(x) Material Temp C. Time min g/min Area 1st 2nd Depletion Content 2%Nickel 750 36 300 0.5252 120 120 0 1.029 Phosphate 2% Cobalt 775 36 1000.5781 118 119 0.0002 1.02 Phosphate 4% Cobalt 700 18 100 0.6287 123 1180 1.069 Nitrate 1% Cobalt 650 36 100 0.8056 115 115 0 1.065 Hydroxide

[0068] While not wishing to be held to any particular theory it isbelieved that the cationic metal species which remain afterdecomposition of the metal compound provide metal-containing cationsbound to the oxygen of the lithium manganese oxide at the surface of thelithium manganese oxide. This is different from forming a simple metaloxide layer over the surface. The cationic metal species which remainafter decomposition of the metal compound, are not thought to simplyremain on the LMO surface as positively charged ions because as suchthey would leave during extraction of lithium during cell operation uponsubsequent activation of the cells. Instead, the positively charged ionsare thought to be incorporated into, in or on the outside layer of thespinel structure. The preferred metals are first row transition metalssuch as titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron(Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). These metalsare thought to form ions which coordinate well with the oxygen at thesurface of the spinel because they have a size roughly comparable to theMn. Some second row transition metals may also be included and areselected from zirconium (Zr), molybdenum (Mo), palladium (Pd), cadmium(Cd), tungsten (W), and platinum (Pt). In addition, othernon-transition-metal metals are used. They include those metals capableof a +3 valence state such as aluminum. Other metals such as tin arealso possible.

[0069] It is thought that upon being heated, the metal compound, when itreaches the melting point, actually decomposes and leaves the metal ormetal-containing group (species) behind. In one embodiment, the metalcompound is a salt. Here, the anion is the component which is driven offby heat. A variety of anions are usable to provide decomposition of thecompound at temperature ranges described herein. Examples includechlorine, carbonate, and nitrate. The metal is dispersed preferablyuniformly on the surface of the spinel, and reduces the surface area. Inan optimized condition, the remaining metal provides an essentiallycomplete coating to provide as low a surface area as possible. However,excess deposited metal or metal species is undesirable because the addedweight adversely affects the specific capacity of the cathode activematerial. It is preferred to use a metal salt, preferably a transitionmetal salt, that melts or essentially reacts in the presence of the LMOto achieve decomposition at a preferred temperature of about 400° C. toabout 500°C. Although, the manner in which the metal cation isincorporated on the outside layer of the spinel structure is not clearlydefined, its presence has been documented by analysis as per theExamples and Table 2. The surface-area-reducing effect is clearlyevident. The fact that the metal compound decomposition does not resultin an increase in surface area is an indication that it does not resultin formation of a separate metal oxide compound at the surface. This isbecause the formation of a separate metal oxide compound would, asunderstandable by those skilled in the art, result in an increase insurface area. Therefore, it is clear that the metal is somehowincorporated into the spinel structure most likely by reacting with theparticle terminus groups of carboxyl, carboxyllic, or hydroxyl groups.Based on scanning electron microscope (SEM) the surface of the particleslooks polished. Continued heating beyond this is not desired since itleads to metal ion diffusion away from the surface and cause the surfacearea to increase. While not wishing to be held to any theory, it appearsthat the metal to some extent goes down on the outer layer of the spinelcrystal attached to an oxygen of the outer layer of the spinel at theterminals of lattice where the spinel ends in alternating two oxygensand one manganese. It is thought that the most likely place for themetals to attach is to the terminal oxygens of the lattice as evidencedby the fact that it is not possible to simply rinse away the metalcations after their deposition thereon from decomposition of the metalcompound. If the metal cation were merely a plain ion, it would bepossible to simply rinse it off.

[0070] The beneficial result of the deposition of metal at the surfaceis clear from the data described above; it reduces the surface area ofthe overall spinel, and each example demonstrates lower surface areathan the initial untreated spinel. Each treated example also showsbetter ion transport, less corrosion, and better cycling. In addition,the unexpected advantage of extra capacity is achieved. This appears toprovide the ability to access more of the lithium. In other words, it ispossible to obtain more capacity from the LMO after treatment than wouldhave been possible from the LMO starting material, as-received from thevendor, and conventionally made. From the experiments described above,it is clear that the capacity always exceeds that of the untreatedspinel regardless of what metal is used. Therefore, one thing is clear,that it is very important to incorporate the metal into the spinel. Thesize of the incorporated metal is related to its ability to achievebeneficial results. Therefore, first row transition metals arepreferred.

[0071] The anion of the metal compound is important only to the extentthat the compound itself must be decomposable at a temperature belowwhich the original spinel starts losing oxygen or the lithium becomestoo mobile. Therefore, the lower the temperature at which the anionportion decomposes, the more attractive is its use. Metal compoundswhich are metal oxides are known to be very stable and only decomposableat very high temperatures on the order of 900° C. In the presentinvention, the compound decomposes at a temperature less than 900° C.,desirably less than 800° C., more desirably less than 750° C., mostdesirably less than 650° C., and preferably less than 600° C. Morepreferably the metal compound decomposes at a temperature less than 550°C. Some metal compounds are even capable of decomposing at a temperatureas low as about 300° C. to about 350° C. A decomposition temperature ina range of about 400° C. to about 500° C. is suitable. The metalcompounds, for use in the invention, may be pre-screened by determiningtheir melting point, their decomposition temperature, and by conductingthermal gravimetric analysis (TGA).

[0072] In the case of compounds having more that one metal cation it ispossible to deposit more than one metal onto the surface. This occurred,for example, when using lithium aluminum chloride. In the case of acompound such as nickel carbonate, for example, the carbonate anionwould decompose leaving only the nickel. The effect of the depositing ofmetal cations on the surface of the LMO is reduced surface area whichresults in less corrosion of the manganese and better cycling. Bycorrosion of the manganese it is meant that manganese ions are oxidizedand can eventually dissolved away during operation of the battery to theharsh conditions of battery operation. The addition of the metal cationof the invention has the beneficial effect of reducing corrosion of themanganese. The treated lithium manganese oxide of the invention ischaracterized by having extra capacity which seems to cause the abilityto access more of the lithium or operation of the battery. Thus, thereseems to be an enhancement of lithium ion transport and/or removal fromthe cathode. As stated earlier, regardless of the metal used abeneficial effect was observed, and capacity exceeds that of the baseLMO.

[0073] It was noticed that metal compounds decompose very close to theirmelting point. It was also observed that the decomposition of the metalcompound additive occurs at a temperature lower in the presence of thespinel than would occur if the metal compound additive was simplydecomposing by itself. It was observed that some metal salts such as theacetates readily decompose if heated by themselves. For other metalsalts, their decomposition seems to be in conjunction with the lithiummanganese oxide being present. Therefore, decomposition is facilitatedthereby. It was observed that lithium carbonate melts at about 750° C.In the presence of the spinel LMO, the lithium carbonate decomposed at atemperature as low as about 650° C., showing that decomposition of themetal compound is altered by the presence of the starting material LMOspinel. It was observed that the metal cations at the surface areclearly not a metal coating and they somehow combine with the surfacecharge or atomic bonding, or ionic complex with the lithium manganeseoxide. Therefore, the result is a decomposition product of the metalcompound that forms in the presence of the LMO and after suchdecomposition reaction, the surface of the LMO loses some of itsporosity. Under a scanning electron microscope (SEM) LMO particlestreated with aluminum nitrate looked essentially polished demonstratingthe surface area was lowered. It appears that in the process ofdecomposition the metal compound acts as a fluxing agent while thedecomposition reaction is ongoing because some of the gases given offduring decomposition uniquely polish the surface of the LMO. In the caseof a chlorine or nitrate compound, chlorine or nitric oxide gas is givenoff as a reaction occurs, which reduces the terminal groups, the boundwater and causes other related results. Therefore, decomposition gasesreduced the terminal groups and the bound water within or on the spinelitself. As a result, the preferred anions in the metal compound arethose that work best as flux agents. This means they have a greatermobility to move through and affect any porosity of the particles. Thismobility also results in covering as much of the free surface area aspossible to cause a surface reduction effect. It is evident that it isdesirable to drive decomposition reaction to essentially fullcompletion.

[0074] Advantageously, these beneficial effects are achieved inatmospheric conditions. Thus, metal cation of the metal compoundeffectively assumes a desired oxidation state for being maintained atthe surface of the LMO while the reaction is conducted simply in air.Enhanced oxygen content may be beneficial, however, an oxidizing airenvironment was adequate. Another advantageous feature of the method ofthe invention is that the rate of heating and the rate of cooling do notappear to be critical. However, it is preferred that the synthesis beconducted at less than 600° C. Therefore, it is possible to simply heatthe metal compound and the LMO in an oven and at the desired temperaturefor the desired amount of time and then permit it to cool. The addedmetal results in a small dilution effect with respect to the atomicweight proportion of the lithium. In a conventional starting materialspinel the amount of lithium initially is expected to vary betweenLi_(x)Mn₂O₄, where x is 1.02 to 1.08. In the case where the added metalcompound does not contain lithium, then the atomic proportion of lithiumin the final treated product will be lessened. If the metal compounditself contains lithium the atomic proportion of lithium and the finalproduct will vary slightly depending on the relative weight of thelithium and other metal cations in the added metal compound.

[0075] Importantly, by the methods of the invention it is possible toachieve the beneficial aspects of enhanced capacity, reduced loss ofcapacity during cycling, reduced surface area, and stabilizing of theLMO against corrosion, without changing the basic spinel structure ofthe original LMO compound as evidenced by no major shifts in the x-raypattern of the treated LMO as compared to the untreated LMO. This isthought to be because the added metal produces a passivation layeraround the LMO particles to provide stability. The manganese alone isnot able to produce such a passivation layer. This distinguishes thelithium manganese oxide from other metal oxides such as lithium cobaltoxide and lithium nickel oxide which are known to be capable ofproducing a passivation layer.

[0076] The methods of the invention are different from other approachesto attempting to improve performance of the LMO. The most commonapproach is to attempt to sinter the LMO at high temperature to achievea more crystalline product by heating to about 800° C. The method of thepresent invention avoids sintering which has certain disadvantagesincluding oxygen depletion. The present method also avoids formingLi₂MnO₃ which has been here found to be undesirable because ofdelithiation instabilities during discharge.

[0077] The amount of additive metal compound necessary to achieve thebeneficial results is not large. The amount added is determined by theamount of surface area reduction desired and the amount effective toessentially polish the surface and plug the porosity and to stabilizeagainst corrosion. Therefore, a surface-area-reducing amount is all thatis required. Based on the experiments described hereinabove, metalcompound additions on the order of 5 wt. % resulting in on he order of 2wt. % metal deposited on the surface provided surface reduction effecton the order of 20-30%. Further optimization is a matter of choice. Itis thought that metal compound additions greater than about 10 wt. %resulting in deposited metal on the order of 4 wt. % is the maximumamount desirable.

[0078] In summary, metals, and preferably transition metals, are used tostabilize the crystal structure of the spinel. This surface treatmentlowers the surface area of the LMO and improves high temperatureperformance. In the case of transition metal treatment, the capacity wasincreased each time. With optimization of the amount of additive andtreatment conditions, the resulting materials approach the theoreticalcapacity of nominal Li₁Mn₂O₄ at 140 milliamp hours per gram. This isparticularly significant since all LMO with high capacity (or lithiumcontent x approaching 1) suffer from very significant capacity fadingduring cycling even at room temperature. In contrast, the LMO materialtreated with metal salts and preferred transition metal salts of theinvention have demonstrated the benefit of high capacity and smallcapacity fade even at high temperature cycling at about 60° C.

[0079] The treated LMO is prepared by heating a mixture of LMO and ametal compound for a period of time and at a temperature sufficient tocause interdiffusion of excess lithium from the LMO spinel, and metalcation from the metal compound, into an interfacial layer therebycreating a new compound of spinel-like structure, possessing reducedsurface area, increased capacity, and improved thermal stability. Theheating is preferably conducted to cause complete reaction of the metalcompound into the surface of the spinel, allowing for the interdiffusionof excess lithium from the spinel into the newly formed surface, therebycreasing an improved spinel-like structure having the advantages statedabove. Prior to reaction, the metal compound powder and the lithiummanganese oxide powder may be mixed together as solids and then reacted.Alternatively, prior to reaction, the metal salt can be dissolved in asuitable solvent, and the LMO thoroughly wetted by the solution beforereaction to ensure near homogeneous dispersion of the additive.Advantageously, the reaction may be conducted in ambient air. Theatmosphere does not need to be oxygen enriched at the temperaturesdescribed here, but inert atmosphere is not recommended. The metalcompounds are preferably selected to decompose at a temperature lessthan 850° C., desirably less than 800° C., more desirably less than 750°C. and to melt at temperatures less than those stated immediatelyearlier. Other metal compounds, with higher melting points and/ordecomposition temperatures, are still able to react with LMO at or belowthe immediately preceding temperatures and they react at the lowertemperatures described herein. Therefore, the criterion is reaction withthe spinel at temperatures less than 850° C., desirably less than 800°C., more desirably less than 750° C., by melting and/or decomposing inthe presence of the spinel LMO. The preference is to cause reaction at atemperature which does not cause spinel oxygen deficiency to become aproblem. Experiments showed that even at 750° C., reaction withphosphate salts did not produce any measurable oxygen deficiency, thatis, less than 0.01%.

[0080] It appears that for many of the additive metal salts, thedecomposition product is primarily the metal cation. This will bond tothe spinel structure via the terminal oxygens of the spinel. Duringnormal synthesis of spinel LMO, the terminal oxygen is usually attachedto a proton (O—H group). This is the most likely position of the metalcation, that is, replace the proton. Depending on its valence, the metalspecies can include both the metal cation and an additional oxygen atom.Alternatively, not all additives decompose completely to the metalcation. For example, the phosphate salts retain their PO₄ groups. Theend effect is lowered surface area of the treated spinel, improvedcapacity, and improved high temperature cycling. The temperature neededfor the decomposition synthesis described here is advantageouslyrelatively low, at 600° C. or less. Temperatures on the order of 350° C.to 450° C. are adequate for many of the salts used here. The lowerdecomposition synthesis temperature eliminates or significantly reducesthe occurrence of oxygen deficiency and/or the production of Li₂MnO₃.Oxygen deficiency is considered a crystal defect and to be avoided inspinel synthesis. Impurities such as Li₂MnO₃ appear prone todecomposition in electrolytes typically used in lithium polymerbatteries. Impurities in cells have proven to shorten the lifeespecially during operation at temperatures above ambient.

[0081] The results of the process of the invention were compared tomerely heating spinel LMO without any additive. In this comparativetest, no surface area change was observed unless heating was conductedto the point where sintering occurred, on the order of over 800° C. Noimprovement in performance was observed. Thus, the additives and methodsof the invention clearly demonstrated effectiveness in reduced surfacearea, increased capacity, and improved high temperature performance.

[0082] While this invention has been described in terms of certainembodiments thereof, it is not intended that it be limited to the abovedescription, but rather only to the extent set forth in the followingclaims.

[0083] The embodiments of the invention in which an exclusive propertyor privilege is claimed are defined in the following claims.

What is claimed is:
 1. A battery having an active material of anelectrode comprising particles of spinel lithium manganese oxide, havingon the surface of each said particle, cationic metal species bound tothe spinel at anionic sites of said particle surface; where saidcationic metal species includes a metal selected from the groupconsisting of transition metals, non-transition-metal metals having a +3valence state, and mixtures thereof; and said active materialcharacterized by a reduced surface area and increased capacity expressedin milliamp hour per gram as compared to said spinel alone.
 2. Thebattery of claim 1 wherein said cationic metal species is selected fromthe group consisting of metal cation metal oxide cation, metal phosphatecation, and mixtures thereof.
 3. The battery of claim 1 wherein saidcationic metal species is a decomposition product of a metal compoundformed on the surface of the spinel particles.
 4. The battery of claim 1wherein the spinel lithium manganese oxide has the nominal formulaLiMn₂O₄.
 5. The battery of claim 1 wherein the spinel lithium manganeseoxide is represented by the formula Li_(1+x)Mn_(2−x)O₄ where x is in arange of about −0.2 to about +0.5.
 6. The battery of claim 5 wherein xis greater than zero and up to about 0.5.
 7. An electrode having abinder, and an active material comprising particles of spinel lithiummanganese oxide having on the surface of said particles ionic metalspecies bound to the spinel at oppositely charged ionic sites of saidparticle surface.
 8. The electrode of claim 7 wherein the ionic metalspecies includes a transition metal.
 9. The electrode of claim 7 whereinthe ionic metal species includes a non-transition metal having a +3valence state.
 10. The electrode of claim 7 wherein the ionic metalspecies is selected from the group consisting of metal cation, metaloxide cation, metal phosphate cation, and mixtures thereof.
 11. Theelectrode of claim 7 wherein the spinel lithium manganese oxide has thenominal formula LiMn₂O₄.
 12. A composition comprising particles ofspinel lithium manganese oxide having on the surface of each saidparticle ionic metal species bound to the spinel at oppositely chargedionic sites of said particle surface.
 13. The composition of claim 12where said ionic metal species includes a metal selected from the groupconsisting of transition metals; non-transition metals having a +3valence state; and mixtures thereof.
 14. The composition of claim 12wherein the ionic metal species is selected from the group consisting ofmetal cation, metal oxide cation, metal phosphate cation, and mixturesthereof.
 15. The composition of claim 12 wherein the spinel lithiummanganese oxide has the nominal formula LiMn₂O₄.
 16. A battery having anactive material of an electrode which comprises the composition of claim12.
 17. A battery having an active material of an electrode whichcomprises the composition of claim
 13. 18. A battery having an activematerial of an electrode which comprises the composition of claim 14.19. A battery having an active material of an electrode which comprisesthe composition of claim
 15. 20. A method of treating particles ofspinel lithium manganese oxide which comprises the steps of: (a) forminga mixture comprising said lithium manganese oxide particles and a metalcompound which includes a metal selected from the group consisting oftransition metals, non-transition metal metals having a +3 valencestate, and mixtures thereof; and (b) heating said mixture for a time andat a temperature sufficient to form a reaction product of the metalcompound and the lithium manganese oxide at the surface of each saidparticle.
 21. The method of claim 20 wherein said heating step isconducted in an air atmosphere.
 22. The method of claim 20 whereinheating is conducted at a temperature in the range of about 200° C. toabout 800° C.
 23. The method of claim 20 wherein the heating isconducted for a time of about ½ hour to about 6 hours.
 24. The method ofclaim 20 wherein the amount of metal compound contained in the mixtureof lithium manganese oxide and metal compound is from about 0.5% toabout 10% by weight of said total mixture.
 25. The method of claim 20wherein the reaction product is a decomposition product of the metalcompound bound to the terminal oxygens of the lithium manganese oxide atthe particle surface.